1. Field of the Invention
The present invention relates to a control device for an automatic transmission and a control method therefor in an automobile.
2. Conventional Art
An example of conventional art of a control device for an automobile using a mechanism of a gear type transmission is disposed in JP-A-2000-65199.
In the above conventional art, a friction clutch is provided at a gear effecting the minimum change gear ratio in the gear type transmission, thereby, during a change gear, an input shaft rpm of the transmission is reduced through coupling with the friction clutch and a torque reduction during the change gear is compensated by a torque transmitted through the friction clutch to achieve a smooth change gear.
When performing a change gear with such gear type transmission, based on the change gear judgement from a control device together with the coupling with the friction clutch, a claw type clutch is generally released to a neutral state and the torque transmission train in the multi stage change gear mechanism is switched to perform a change gear.
In the conventional change gear which is performed by controlling both clutches for the coupling and for the releasing, so called change gear by clutch switching or rebridging, the control is performed so as to prevent a tie-up in which the both clutches are placed in a coupling condition (over lap condition) or to prevent a condition in which the both clutches are placed in a released condition (under lap condition). More specifically, such a control is performed in that a torque capacity of the friction clutch to be coupled is gradually increased and in response to a detection that a predetermined time has passed after a change gear judgement, the claw type clutch is released to a neutral state.
However, because of initial variation due to individual product differences and of characteristic variation due to such as secular change, such as the over lap condition and the under lap condition between the friction clutch and the claw type clutch are caused in the clutch switching change gear, which arises a problem of extremely deteriorating a feeling during the change gear.
Accordingly, an object of the present invention is to provide a control device for an automatic transmission which, at the time of clutch switching change gear of a friction clutch and a claw type clutch, a torque capacity of the friction clutch to be coupled is detected or computed and based on the detected or computed value a timing when the claw type clutch to be released is released into a neutral state is determined, thereby, a stable clutch switching is always realized with respect to initial variation due to individual product differences and characteristic variation due to secular changes thereof and a desirable change gear quality is ensured.
In order to resolve the above problems, the present invention provides a control device for an automatic transmission which comprises a torque transmission means provided between an input shaft and an output shaft of a gear type transmission, wherein the torque transmission means in at least one change gear stage is constituted by a friction clutch, the torque transmission means in the other change gear stages are constituted by claw type clutches and when performing a change gear from one change gear stage to another change gear stage, the friction clutch is controlled, and further comprises, a torque capacity detecting means which detects or computes torque capacity of the friction clutch when performing a change gear to a predetermined change gear stage and a clutch release timing determining means which determines a timing when releasing the claw type clutch into a neutral state based on the value detected or computed by the torque capacity detection means.
Preferably, the torque capacity detection means in the control device for the automatic transmission is a hydraulic pressure sensor.
Further preferably, the torque capacity detection means in the control device for the automatic transmission is an acceleration sensor.
Further preferably, the torque capacity detection means in the control device for the automatic transmission is an output shaft rpm variation rate detector.
Still further, the present invention provides a method of controlling an automatic transmission, which comprises a torque transmission means provided between an input shaft and an output shaft of a gear type transmission, wherein the torque transmission means in at least one change gear stage is constituted by a friction clutch, the torque transmission means in the other change gear stages are constituted by claw type clutches and when performing a change gear from one change gear stage to another change gear stage, the friction clutch is controlled, comprises, the steps of detecting that the friction clutch has acquired a predetermined amount of torque capacity when performing a change gear to a predetermined change gear stage and determining a timing when releasing the claw type clutch based on the detection of the predetermined amount of torque capacity.